This invention concerns cutter bits for the mining industry and is especially concerned with long wall mining bits used in removing coal, potash or trona formations.
Cutter bits used in mining operations are comprised of a shank for insertion into a toolholder with a forward working portion on the shank for engagement with the material formation. An individual insert of hard wear resistant material has been provided on the forward working portion to cut into the coal or mineral formation and to enhance the life of the bit as it removes the mineral formation.
With long wall mining bits, the insert is positioned to face the direction of rotation of the bit and has a cutting edge on the insert impacting the mineral formation. A clearance face is provided behind the insert to reduce the rubbing of the forward working portion against the mineral formation as the bit passes through the formation.
A plurality of the cutters are usually mounted on a drum that typically might be rotated at 60 revolutions/minute while the drum is driven into and along a face of a coal formation at about 20 to 40 feet/minute. The forward working portion of the cutter bits usually penetrate the coal formation by up to two to four inches. The coal formation is removed by the cutting, picking, and hammering of the cutter bits as the drum rotates and is moved along the face.
Typically, in long wall mining of coal formations, the drum may pass along a face of a coal seam with operator access to the drum occurring only at the end of each pass.
As the cutter bit becomes used, wear develops across the forward working portion of the bit extending from the leading cutting edge of the insert rearwardly across the clearance face. The reduced clearance increases the rubbing and abrasion of the forward working portion against the coal formation, generating excessive heat frequently causing the insert to fail due to heat checking. As the wear scar develops across the clearance face of the bits, machine power consumption rises, sometimes stalling the machine.
The cutting edge of the insert on the cutter bits faces in the direction of rotation of the bit and, when viewed from a front view, the cutting edge tapers outwardly toward the shank and is preferably V-shaped or U-shaped with the V or the U opening toward the shank of the bit. It is desirable to keep this configuration for the life of the bit rather than to let the cutting edge wear to a flat. When the cutting edge does wear to a flat, not only is more power required, but more dust is also created in the mine.
It is an object of the present invention to provide a cutter bit that is more durable than previous mining bits.
It is a further object of the present invention to enhance the life of the cutter bits by reducing the heat generated by the rubbing of the clearance face against the coal formation.
It is still a further object of the present invention to enhance the life of the cutter bits by minimizing the propagation of cracks due to heat checking of the carbide.
It is still a further object of the present invention to enhance the life of the cutter bit by controlling the wear of the clearance face so as to provide a self-sharpening cutter bit.
It is a further object of the present invention to make the life of the cutter bit more predictable, enabling bit changes to be made at the end of a pass, when the cutter drum is more accessible.